The invention relates to a circuit arrangement for a hydraulic drive as controlled system.
In numerous drives, in particular hydraulic cylinders, it is necessary for the component to be moved by the drive to be moved with high accuracy as regards speed and position. This applies to a particular extent in continuous-path controls in which a plurality of drives, provided for example for driving tools or workpieces in several axes, are to be driven in mutual geometrical dependence. An example of such a continuous-path control is the non-cutting deformation in the production of rims.
For controlling the fluid paths between the hydraulic drive and a fluid source or a tank in each case a servo or proportional valve is provided. Due to the non-linearity of the valve characteristic and counter forces and frictional forces acting on the drives a lag error difference of the drives with respect to each other occurs so that therefore a drive lags behind another drive in its movement.
To avoid such contour or lag error differences it is not sufficient to provide for the path control a closed-loop control in which the actual value of the position of the hydraulic drive is detected as controlled variable. For example in a system using a displacement pickup and a comparator for comparing the controlled variable with the desired value of the position a control deviation is formed which is converted in a control amplifier to a manipulated variable with which the valve is driven. Even when the control or servo amplifier is constructed as controller with observer for taking account of the peculiarities of the hydraulic controlled system such a lag error difference cannot be avoided.
The invention is thus based on the problem of further developing the circuit arrangement in such a manner that the lag error difference arising in such continuous-path controls is avoided. The constructional expenditure is to be small and the circuit arrangement is to be suitable for path control in driving drives with several axes.